1. Field of the Invention
The invention relates to hydrodynamic brakes and in particular to hydrodynamic brakes having rotor and stator blades.
2. Description of Related Technology
Fluid-filled hydrodynamic brakes having a rotor and a stator, each having a plurality of blades, are known in the art. For example, such a brake is disclosed in DE 31 13 408 (corresponding to Vogelsang, U.S. Pat. No. 4,474,270).
Hydrodynamic brake development has focused on the achievement of high density power absorption. Therefore, the brake components (especially the rotor and the stator) have been designed with a view toward having these components participate as much as possible in energy exchange. Attempts have also been made to design a brake in such a way that it can be operated in a desired manner at various operating states.
The high density power absorption attained by such brakes has led to a correspondingly high load on the components involved in oil conduction. As a result, the brakes are noisy which is undesirable for street traffic, especially when the brakes are utilized in buses.
Attempts have been made to reduce the noise level produced by such brakes during their operation while simultaneously maintaining high density power absorption. However, only secondary measures have been attempted which do not address the production of noise, only its effects. Such attempts have included making the housing parts thicker or providing insulating sheaths that surround the entire brake. Both of these measures are relatively expensive, require significant assembly work, increase the area required for the structure (which is especially undesirable) and have not been very effective.
If the acoustic problem is considered alone, it might appear desirable to reduce the number of blades of the rotor and stator in order to reduce the frequency of the periodically recurring flow shocks (i.e. flow impacts) in the brake and thereby reduce the noise made by the brake. However, if the number of brake and stator blades are reduced, but the energy density (and thus the power uptake) of the brake is not likewise reduced, an increase of the energy of the flow shocks occurs resulting in even stronger excitation (i.e. vibration) of the brake components, as well as of the oil flow, producing increased noise. To date, there have been no measures which directly address the root of this problem.